Democratic Senator Mark Pryor filed his paperwork on Friday.
At the Pryor campaign headquarters, the two-term senator spoke about the campaign that's unofficially been underway on the airwaves for months.
"This race is about Arkansas," Pryor said on Friday, "It's not about all this outside money. We can't compete with all this outside money. This is about the people around the state and what kind of senator they want and the priorities they want to see in a senator in Washington."
Pryor is expected to face Republican Congressman Tom Cotton in the general election in November.
Neither Pryor nor Cotton faces a primary challenger.
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